The present invention relates to a sheet accumulation apparatus by which sheets are sequentially discharged from an image formation apparatus for example through a paper ejection opening into a tray means. The present invention relates to an improved tray elevating mechanism by which a tray means on which a large amount of sheets is loaded can be easily transported out of the apparatus.
Generally, this type of sheet accumulation apparatus is widely known as an apparatus by which sheets discharged from an image formation apparatus (e.g., printing machine, copier) are loaded and stored in a tray means provided at the lower side of a paper ejection opening. Then, the apparatus for accumulating therein a large amount of continuously discharged sheets elevates this tray means in accordance with the load amount. When this tray is full or when a job is completed, a user takes the sheets out of the tray.
When a large amount of sheets are taken out of the tray as described above, the sheets are transshipped to a hand truck for example. A technique for simplifying this transshipment is disclosed, for example, in Japanese Patent Laid-Open No. 2000-143070 (Patent Publication 1). This publication discloses an apparatus by which a tray is separated from a lift mechanism for elevating the tray to load sheets in a pallet-like manner and, when the sheets are taken out, a hand truck for transportation is positioned and set below the lift mechanism and the tray descended by the lift mechanism is moved on the hand truck and is moved out of the apparatus.
Thus, according to the apparatus of this publication, a tray  and an elevating mechanism (elevator mechanism) are provided at a position protruding from an apparatus housing to outside, a hand truck is positioned and set below a tray in which sheets are loaded, and the tray is descended onto the hand truck to automatically transship the tray into the hand truck. In this manner, sheets in the tray can be transported to outside without being transshipped to a transport apparatus such as a hand truck. In order to secure the transshipment of this tray, the accumulation apparatus includes a positioning mechanism for positioning and setting a truck at a predetermined transship position and a sensor for detecting a hand truck set at this position.
As described above, Patent Publication 1 as described above, for example, suggests a technique for separating a tray in which sheets are loaded from an elevating arm for supporting and elevating this tray to accumulate sheets in the tray to transship the tray in which the sheets are loaded into a transportation hand truck in a pallet-like manner to discharge the tray out of the apparatus. In this case, a transportation hand truck 90 has been conventionally structured, as shown in FIG. 9(a), so that a back face of a flat plate-like bottom plate 91 includes a plurality of wheels 92 and an upper face 91a of this bottom plate has thereon a tray member 93 and the bottom plate 91 is integrated with a handle 93 pushed by hands. An elevating arm 94 includes two fork members 94a and 94b connected to an elevating mechanism and the fork members 94a and 94b enter a stepped space 95 formed between the bottom plate 91 and the tray 93 of the hand truck.
Thus, a distance H between the sheet storage position of the tray 93 and a contact face can be calculated by: H=H1 (tray elevating height)+H2 (tray attachment/detachment height). This tray attachment/detachment height can be calculated by H2=h1 (wheel height)+h2 (bottom plate height)+h3 (fork insertion height). The hand truck structure as described above is disadvantageous in that a high tray attachment height causes a dead space, causing  a larger size of the apparatus. For example, when heights of a paper ejection opening and an installation surface (which are equal to the above distance L, respectively) are set to be a predetermined value, a tray elevating height (H1) to which the tray is elevated in order to load sheets can be calculated by H1=(H−H2). Thus, a disadvantage is caused where a high tray attachment/detachment height (H2) reduces the maximum amount of a load that can be stored in the tray.
This invention has been made in view of the above problem. It is the first object to provide a sheet accumulation apparatus having a structure by which a tray in which sheets are loaded is discharged by a transportation carrier out of the apparatus. This sheet accumulation apparatus can secure, without having to increase the size thereof, the maximum load amount of sheets that can be loaded in the tray. Thus, this sheet accumulation apparatus can have a compact size and a large amount of sheets can be loaded therein.
It is the second object to provide a sheet accumulation apparatus by which a pile of sheets can be prevented from being collapsed when a tray in which sheets are loaded is moved from elevating arms of the apparatus to a transport carrier, and an image formation apparatus including this sheet accumulation apparatus.
Other objects and features of this invention will be clear from the following description of illustrative embodiments with reference to the attached drawings.